Gear pump with externally adjustable shroud



Feb. 25, 1958 i 0, BANKER 2,824,524

GEAR PUMP WITH EXTERNAL-LY ADJUSTABLE SHROUD Filed Jan. 18, 1955INVENTOR. Oscar fl, Banker BY W 5 United States Patent GEAR PUMP WITHEXTERNALLY ADJUSTABLE SHROUD Oscar H. Banker, Evanston, 11]., assignorto New Products Corporation, Skokie, 111., a corporation of DelawareApplication January 18, 1955, Serial No. 482,471

3 Claims. (Cl. 103-126) This invention relates to a gear type pump andparticularly to an externally adjustable shroud for the teeth thereof.

The volumetric efliciency of a gear type pump depends upon the closenessof the fit between the tips of the gear teeth and the enclosing shroud.This presents a manufacturing problem in that .close tolerances must ,bekept between the component parts of the pump .or alternatively, ordinarytolerances may be kept, with errors tending toward a closeness of fitand the parts subsequently run in until they run freely. This alsopresents a maintenance problem after the pump has been run a long timeand the clearance between the teeth and ,snroud nas bgcome enlarged andthe volumetric efficiency has 'fallen o The obvious solution to themaintenance problem is to dismantle the pump, remove the worn shroud .orgears, or'both, and replace them with correspondingnew elements whichfit together with the desired closeness to produce the originalvolumetric efliciency. This ,solution requires a shut-down time longenough to perform the necessary exchange of new parts for the worn .oneswhich is costly, to which is added the cost of the labor involved.

In other designs, the closeness of the fit is assurejd'by providing ashroud which is held against the gear teeth by the fluid under pressure.This construction willmaintain a large measure of the initial volumetricetficiencybut the continuous pressure accelerates wear between theinsert and the gear teeth, and frequent replacement of the insert isthen required. In addition, the friction forces developed between theinsert and the gear teeth increases the amount of power required todrive the pump and hence although the volumetric efficiency may bemaintained at a relatively high level, the working efficiency, that is,the energy in the fluid pumped divided by the energy expended to drivethe pump becomes undesirably small.

An object of this invention is the provision oifa gear type pump whichmay be readily manufactured to have a high volumetric efliciency withoutrequiring that excessively close tolerances be used in its manufacture.

Another object of this invention is the provision ,of a gear type pump,the volumetric efficiency of which may be readily and quickly restoredafter use without completely dismantling the pump and without replacingany of the major parts thereof.

Another object of this invention is'the provision of a gear type pumpwherein the shroud used around the gears to separate the high and lowpressure zones is held in position by the fluid under pressure, .but themovement is limited by a stop, the position of which relative to -theframe or housing of the pump'may be readily adjusted from the exteriorof the pump.

As a specific object, this invention seeks to provide a gear type pumphaving 'a single piece shroud for the low and high pressure zones, withmeans for adjusting the position of the shroud relative to thezge'arssuch that ice to provide a gear type pump having a single piece shroud"for the high and low pressure zones thereof wherein the positionvof'the shroud relative to the gear teeth is determined partly by thepressure of the fluid being pumped, and partly by an adjustable plugaccessible from the exterior of the pump for limiting the movement ofthe shroud under fluid pressure, the position of the plug :in thehousing being determinable by appropriate gage means withoutdisassembling the pump. I

These and other objects of this invention will become apparent from thefollowing detailed description when taken together-with the accompanyingdrawings in which,

Fig. 'l is an elevation in section through the pump;

'Fig. '2 is a side elevation of the pump with the cover plate removed;

'Fig. 3 is a bottom'view of the pump partly in section, the view beingtaken along line 3-6 of Fig. 1;

Fig. '4'is a greatly enlarged fragmentary side elevational view, partlyin section of the left-hand portion of Fig. 2; and Fig. 5 is a stillfurther enlarged fragmentary sideelevational view of a portion of Fig. 4showing the means'by which an adjustment can be made in the pump.

Referring now to the drawings for a detailed descrip- "tion of theinvention, the pump is comprised ofa housjing 10 having a circularcavity 11 formed in the righthand side thereof as viewed in Fig. l, forthe reception .of adrive gear 12 and .a driven gear 13 meshingtherewith. Drive gear 12 is mounted on .a drive shaft 14 whichextends tothe left as viewed inFig. .1 through an opening 15 formed in casting 10to the exterior where it maybe reached by any suitable drive mechanism(not.shown). Shaft 14 drives gear 12 through a key 16 and is supportedin housing 10 by suitable ,needle bearings 17, '18 disposed on eitherside of gear 12.

Cavity '11 is closed by a cover plate 19 having a recess 20 within whichneedle bearing 18 is .disposed, and a second recess '21 within which isdisposed the right hand end as viewed in Fig. l of a pin 22 on which.gear 13 is mounted through the intermediary of bearings 23,. Theleft-hand end of pin 22 as viewed in Fig. .1 extends into acorresponding recess 24 in housing 10. Cover 'plate 19 is secured tohousing 10 by appropriate bolts :25 disposed in bosses "26 formed aroundthe periphery of housing 10.

, The sides of gears '12 and 13 are sealed by plates 27 .and 28 disposedin cavity 11 one on either side of the gears. No seals are providedbetween plate 27 gandeither the housing or the gears since .the only wayin which 'fluid can escape from the housing .to theleft as viewed inFig. 1 is along shaft 14 and said shaft .14 is sealed with respect tothe pump by a lip-type seal 29 in the customary manner. Plate 28 is.sealed with respect to housing 10 and cover plate 19 by an O-ring seal30. A seal is effected between plate 28, pin .22 and ,cover plate 19 by01ring31, and between plate 28, bearing 18 and .cover plate 19 by.O-ring '32, the O-rings encircling pin 22 and bearing 18, respectively.It is contemplated that the thickness of each O-ring 30, .31 and '32,will'be substantially the same and that it will be greater than theaxial dimension of the recesses .in which said O-rings are retained suchthat by drawing up bolts 25 to the requisite pressure the O-rings willbe compressed and will provide the desired seals without effectingcontact between-cover; plate 19 and side seal plate 28.

It may be noted that shaft 14 may-move-axi'ally in its openings 1 5 and20 and that gear 13 may move =axially;relative to its pin 22 so thatthe-pressure exerted "by :coverzplate 119 through the O-tings upon sidesealing Theinlet and outlet openings for the pump are shown with highpressure openings 43 and 41.

plate 28 is transmitted through the gears to side sealing plate 27 torender said side sealing plate 27 effective to prevent leakage frombetween the gears through the housing and opening 15. Thus seal 29 isnot required to withstand full pump pressure at any time.

The low and high pressure zones around gears 12 and 13 are defined by asingle shroud 33 which may have a substantially cylindrical outersurface 34, the diameter of which is less than the diameter of cavity11. An opening 35 is formed on the interior of shroud 33, said openingbeing contoured to form pockets 36 and 37 designed to fit closely aroundthe peripheries of gears 12 and 13, respectively, for approximately 180of the circumference thereof, a high pressure cavity 38 and a relativelylarge low pressure cavity 39. p

more clearly in Fig. 3. The inlet opening is shown at 40 in housing 10,side seal plate 27 having a corresponding opening 42 to provide apassageway from cavity 39 in shroud 33 to the exterior of the pump. Theoutlet opening is shown at 41 and it is aligned with an opening 43 inside seal plate 28 which in turn is i communication with the highpressure cavity 38 in shroud 33. Suitable pipe connections can be madeto the inlet and outlet openings 40 and 41 as desired.

It may be observed that the space between side seal plate 28 and coverplate 19 is in direct communication Fluid pressure therefore acts uponplate 28 to urge the plate to the left as viewed in Figs. 1 and 3 tomaintain the seal between the side seal plates 27, 28 and the sides ofgears 12 and 13. Excess pressure upon the gears is prevented, however,by the intervening shroud which acts as a stop to limit the movement ofplate 28 toward plate 27.

The adjustability of shroud 33 relative to gears 12 and 13 is providedby means now to be described. It may be appreciated that with fluidunder pressure in the high pressure cavity 38, shroud 33 will behydraulically unbalanced in a direction toward the left as viewed inFig. 2. This will cause the shroud to engage the peripheries of theteeth of gears 12 and 13 on the right-hand side thereof to form a fluidtight seal thereat. It is undesirable, however, to have full pumppressure acting upon shroud 33 since to do so would create an excessiveamount of wear between the teeth peripheries and the shroud and wouldalso increase the power required to drive the pump. The movement ofshroud 33 toward the gear teeth is therefore limited by a stop in theform of a plug 44, preferably of cylindrical form for ease ofmanufacture, which is retained in a' correspondingly formed opening 45the axis of which bisects, and is perpendicular to, a line conneetingthe centers of pump gears 12 and 13. This position of plug 44 results ina substantially equal pressure being exerted upon both gears 12 and 13by the shroud to provide uniform wear of the gear teeth peripheries.Uniformity of wear is still further assured by causing the flatright-hand end 46 of plug 44 as viewed in Figs. 2 and 4 to bear againsta flat surface 47 formed in the outer periphery of shroud 33 adjacentplug 44. A fluid tight seal is provided between plug 44 and housing byan O-ring 48 retained in a groove 49 formed peripherally of plug 44.

Movement of plug 44 to the left as viewed iniFigs. 2 and 4 in responseto fluid pressure insofar as permitted lbywear between the gear teeth ongears 12 and 13 and shroud 34 is prevented by a clamp plate 50 which ex-'tends across opening 45 and is secured to housing 10 by appropriatebolts 51. In accordance with the objects of this invention, however,plug 44 does not necessarily contact clamp plate 50 directly, but isseparated therefrom by a plurality of shims 52 shown more clearly inFig. 5. These shims may be disc-shaped and either of the same thicknessor of differing thicknesses depending upon the depth of the spacebetween the end of plug 44 and plate 50. Thus, shims '52'rnay comprise aplurality of discs of one-thousandths of an inch thickness each, thenumber used being suificient to hold shroud 33 at the point wherecontact between the shroud and the gear teeth on the right-hand side ofthe gears as viewed in Fig. 2 is just barely established.

The number of shims, or the depth to be accounted for by the shims, isdetermined by inserting a gauge of the depth micrometer type having amovable central rod 58 and an anvil 53 extending to either side of saidrod so as to contact the face 54 of casting 10. It is understood thatface 54 is ground perfectly flat and smooth and at right angles to theaxis of plug 44 so that the gauge will give a true reading. With rod 58inserted in opening 45 until it contacts plug 44 while anvil 53 contactsface 54 the gauge is removed and the distance between the end of plug 44and the face of the anvil 53 which contacted face 54 is then measured,or is read from the calibrated barrel of the micrometer, and -acorresponding thickness of shims 52 is inserted in opening 45 adjacentplug 44. Clamp 50 is then placed over the opening without any gasket andbolts 51 are tightened upon plate 50.

Inasmuch as the selection of the thickness of shims is done after thepump is assembled, it is important that the position of shroud 33 incavity 11 be definitely known,

and preferably, that its position be such as to cause it to contact theperipheries of the gears teeth 12 and 13 on the right-hand side of thegears as viewed in Fig. 2. This is accomplished by inserting acompression spring 55 into a recess 56 formed in the right-hand side ofshroud 33 as viewed in Fig. 2, the spring being compressed betweenshroud 33 and the inner wall of cavity 11 in housing 10. Spring 55,therefore, exerts a constant pressure upon shroud 33 so that in theabsence of fluid pressure developed by the operation of the pump, theshroud will nevertheless be urged to the left as viewed in Fig. 2against the right-hand side of gears 12 and 13 with a light pressuredetermined by the selected characteristics of the spring.

The space between the outer periphery of shroud 33 and the cylindricalwall of cavity 11 is in communication with the low-pressure zone througha slot 57 extending from the exterior of the shroud to the saidlow-pressure zone. Any fluid leaking out of the high-pressure zone maytherefore be conducted back into the low-pressure zone where it is againoperated upon by the gear teeth.

The pump construction hereinabove described provides a means forrestoring a worn pump to substantially its initial volumetric efficiencywithout dismantling the pump and without replacing any of the wornparts. All that is required is that bolts 51 be withdrawn and clamp 50be removed from across opening 45, whereupon the thickness of the spacebetween the lefthand end of plug 44 as viewed in Fig. 4 and faces 54 canbe accurately determined by a gauge as aforesaid and the appropriatethickness of shims inserted into said opening. Spring 55 will insure theproper location of shroud 33 relative to gears 12 and 13 during themeasuring operation so that upon inserting the appropriate thickness ofshims and replacing plate 50, the pump is againready to operate and itsvolumetric efliciency will be substantially the same as when the pumpwas new.

It may be noted that duringthe operation of the pump, gears 12 and 13will be urged, apart by the fluid under pressureto the, extent permittedby the looseness of the fit between the gears and their bearings. Thistendency of the gears to separate causes the outer peripheries of theirteeth to approach more closely the adjacent walls of gear cavities 36,37 and thus assists in reducing leakage around the gears and inimproving the volumetric efliciency of the pump.

Another beneficial result flowing from the above described design ofshroud and gears is that all working surfaces can be made of high gradematerial such as hardened and ground steel or steel alloys for longwear,

While the pump housing, having no working surfaces, can be made as a diecasting for low cost manufacture.

It is understood that the foregoing description is merely illustrativeof a preferred embodiment of this invention and that the scope of theinvention therefore is not to be limited thereto, but is to bedetermined by the appended claims.

I claim:

1. In a pump having a housing defining a cavity, a drive gear in thecavity, a driven gear meshing with the drive gear, inlet and outletopenings in the housing adjacent the gears, a shroud surroundingportions of both gears and separating the pressure side of the gearsfrom the suction side thereof, said shroud having a contoursubstantially the same as that of the cavity and fitting loosely in thecavity in a direction transverse to the axes of the gears, said shroudfurther having openings in alignment with the inlet and outlet openingsof the housing, resilient means urging the shroud toward one side of thegears, a movable stop on the housing adapted to contact the shroud tolimit the movement of the shroud toward the said one side of the gears,said housing having an access opening from the exterior thereof to thestop, a cover plate for the opening, and means insertable through saidopening and filling the space between the stop and cover plate foradjusting the location of the stop relative to the gears.

2. A pump as described in claim 1, said stop comprising a cylindricalplug, the opening therefor in the housing likewise being cylindrical,the means insertable through said opening comprising one or more discsof predetermined thickness, and means for effecting a fluidtight sealbetween the plug and housing.

3. A pump as described in claim 1, the cavity in the housing beingsubstantially circular in cross-section and the shroud being likewisesubstantially circular in crosssection and being of slightly smalleroutside diameter than the diameter of the cavity.

References Cited in the file of this patent UNITED STATES PATENTS1,880,108 Ross Sept. 27, 1932 1,897,560 Lawser Feb. 14, 1933 2,321,609Marco June 15, 1943 2,504,230 Smith Apr. 18, 1950 2,697,987 Barclay Dec.28, 1954 FOREIGN PATENTS 108,394 Great Britain Aug. 9, 1917

